Positive temperature coefficient current source with low power dissipation

Abstract

A positive temperature coefficient current source having reduced reference current requirements. The output transistors are each buffered by another transistor in a Darlington pair configuration. The reference current required for the circuit is reduced while maintaining a positive temperature coefficient for the current source.

I claim: 
     
       1. A positive temperature coefficient current source comprising: a first transistor having a collector for receiving a reference current, a base connected to the collector and an emitter;   a second transistor having a base connected to the base of said first transistor, a collector and an emitter;   a third transistor having a base connected to the emitter of said second transistor, a collector connected to the collector of said second transistor and an emitter;   a fourth transistor having a collector connected to the emitter of said first transistor, a base connected to the emitter of said third transistor and an emitter connected to ground;   a fifth transistor having a base connected to the emitter of said first transistor, a collector and an emitter;   a sixth transistor having a base connected to the emitter of said fifth transistor, a collector connected to the emitter of said third transistor and an emitter; and   a resistor connected between the emitter of said sixth transistor and ground.   
     
     
       2. The current source of claim 1 wherein the emitter of said sixth transistor has an area and the emitter of said third transistor has an area such that the area of the emitter of said sixth transistor is larger than the area of the emitter of said third transistor. 
     
     
       3. The current source of claim 2 wherein the emitter of said sixth transistor is six times as large as the area of the emitter of said third transistor. 
     
     
       4. The current source of claim 1 wherein the collector of said fifth transistor is connected to the emitter of said second transistor. 
     
     
       5. A positive temperature coefficient current source comprising: a first transistor having a collector for receiving a reference current, a base connected to the collector and an emitter;   a second transistor having a base connected to the collector of said first transistor, a collector and an emitter;   a third transistor having a base connected to the emitter of said second transistor, a collector connected to the collector of said second transistor and an emitter;   a fourth transistor having a collector connected to the emitter of said first transistor, a base connected to the emitter of said third transistor and an emitter connected to ground;   a fifth transistor having a base connected to the emitter of said first transistor, a collector connected to the base of said third transistor and an emitter;   a sixth transistor having a base connected to the emitter of said fifth transistor, a collector connected to the emitter of said third transistor and an emitter; and   a resistor connected between the emitter of said sixth transistor and ground.   
     
     
       6. The current source of claim 5 wherein the emitter of said sixth transistor has an area and the emitter of said third transistor has an area such that the area of the emitter of said sixth transistor is larger than the area of the emitter of said third transistor. 
     
     
       7. The current source of claim 6 wherein the emitter of said sixth transistor is six times as large as the area of the emitter of said third transistor.